1. Field of the Invention
The present invention generally relates to a plasma processing apparatus. More particularly, the present invention relates to a plasma processing apparatus capable of detecting high-frequency characteristics specific to the apparatus and evaluating process performance based on the detected high-frequency characteristics.
2. Description of the Background Art
There are many processes using plasma such as etching, thin film formation and sputtering in a manufacturing process of a semiconductor device, a liquid crystal display (LCD) and the like.
In these processes, high-frequency power is externally applied to a processing chamber for conducting the processes, whereby plasma is generated therein. In order to efficiently supply the high-frequency power for generating plasma from a high-frequency power supply source to the processing chamber, an impedance matching circuit is provided between the high-frequency power supply source and the processing chamber. The impedance matching circuit is formed by a variable inductance element, a variable capacitance element and the like.
In a plasma processing apparatus for conducting various processes by using plasma, it is important to maintain constant process performance in order to produce products with high yield. Mass production of the products is realized with a plurality of plasma processing apparatuses. It is therefore necessary to prevent the process performance from varying between the plasma processing apparatuses.
However, it is difficult to detect a change in process performance with time and variation of process performance between the plasma processing apparatuses. Therefore, the constant process performance is conventionally maintained by conducting maintenance of the plasma processing apparatus when defective products are produced by that apparatus. Alternatively, constant process performance is maintained by empirically predicting the period during which the process performance will not change and periodically conducting maintenance of the plasma processing apparatuses based on the predicted period.
Japanese Patent Laying-Open No. 11-121440 discloses a method for evaluating a plasma processing apparatus and a process by detecting an electric change of a high-frequency power feeding system for feeding high-frequency power to a processing chamber.
Referring to FIG. 29, a plasma processing apparatus 300 includes a chamber 250, a discharging electrode 251, a table 253, a monitor 254, a matching circuit 255, a high-frequency power supply source 256, and a computer 257.
Discharging electrode 251 is provided on table 253. Monitor 254 is connected to discharging electrode 251, and measures the impedance of plasma Q as an electric physical quantity upon generation of plasma Q.
Matching circuit 255 is connected between monitor 254 and high-frequency power supply source 256, and conducts impedance matching in order to efficiently supply high-frequency power from high-frequency power supply source 256 to chamber 250.
High-frequency power supply source 256 is connected between matching circuit 255 and a ground node GND, and generates high-frequency power. Computer 257 is connected to monitor 254, and evaluates the plasma processing apparatus and process performance based on the impedance measured by monitor 254.
With a semiconductor wafer 252 placed on discharging electrode 251, high-frequency power supply source 256 outputs high-frequency power, and matching circuit 255 conducts impedance matching in order to efficiently supply the high-frequency power from high-frequency power supply source 256 to chamber 250. The high-frequency power is supplied to discharging electrode 251 through monitor 254, whereby plasma Q is generated in chamber 250. In this case, chamber 250 contains a reactive gas for etching, thin film formation or the like. Therefore, semiconductor wafer 252 is etched with the generated plasma Q.
After plasma Q is generated, monitor 254 measures the impedance of plasma Q, and outputs the measured impedance to computer 257. Computer 257 evaluates plasma processing apparatus 300 and process performance thereof based on the measured impedance received from monitor 254.
Japanese Patent Laying-Open No. 2000-269195 discloses a method for detecting both a change in plasma processing characteristics of a semiconductor wafer with time and the timing of cleaning the inside of a vacuum container. In this method, the change in plasma processing characteristics with time and the cleaning timing are detected by measuring the impedance of plasma in a plasma processing apparatus, a peak-to-peak voltage of a high-frequency voltage, and a self-bias voltage generated at an electrode receiving the high-frequency voltage.
However, the methods disclosed in the above Japanese Patent Laying-Open Nos. 11-121440 and 2000-269195 measure impedance of plasma generated in the plasma processing apparatus, impedance specific to the apparatus which is determined by the geometry of the plasma processing apparatus, and the overall impedance including impedance of a high-frequency power feeding portion i.e., a portion from the impedance monitor for monitoring the impedance of plasma to the plasma processing apparatus.
FIG. 30 shows an equivalent circuit upon generation of plasma. Referring to FIG. 30, a circuit 210 is an equivalent circuit of a matching box, a circuit 220 is an equivalent circuit of a coaxial cable from circuit 210 to the processing chamber, a circuit 230 is an equivalent circuit within a processing chamber, and a circuit 240 is an equivalent circuit of a grounding system.
Circuit 210 has impedance ZM. Circuit 220 has impedance ZC. Circuit 230 has impedance ZQ. Circuit 240 has impedance ZE. A high-frequency power supply source 200 is connected between ground node GND and circuit 210, and outputs high-frequency power.
The high-frequency power from high-frequency power supply source 200 is supplied to circuit 230 as a processing chamber through circuits 210, 220. A return current flows toward ground node GND of high-frequency power supply source 200 through circuit 240 as a grounding system.
Accordingly, the impedance upon generation of plasma includes impedance to the processing chamber which is determined by impedances ZM, ZC, impedance of plasma which is determined by impedances ZQ, ZE, and impedance specific to the apparatus.
Accordingly, the conventional methods cannot extract only the impedance specific to the apparatus.